1. Field of the Invention
This invention relates to an organic electroluminescent device (to be referred to as organic EL device, hereinafter) using organic compounds and more particularly, to an organic EL device having a modified electrode-organic layer interface.
2. Background Art
Recently, active research works have been made on organic EL light emitting devices. As a basic configuration, the device is constructed by using a transparent electrode of tin-doped indium oxide (ITO) as an anode, forming a hole transporting material such as triphenyldiamine (TPD) thereon by vacuum evaporation, depositing a fluorescent material such as an aluminum quinolinol complex (Alq3) as a light emitting layer, and forming an electrode (cathode) from a metal having a low work function such as magnesium. Attempts have been made to enhance the efficiency of hole injection by successively providing a plurality of organic layers such as a hole injecting layer, hole injecting and transporting layer, and hole transporting layer between the electrodes and the light emitting layer in accordance with the level of electron affinity or ionization potential in order to increase the luminous efficacy. These organic EL devices are attractive in that they can achieve a very high luminance ranging from 100 to 10,000 cd/m.sup.2 with a drive voltage of approximately 10 volts.
The anode for supplying holes to the light emitting layer is formed of transparent conductive materials such as tin-doped indium oxide (ITO) because of the conventional construction that emitted light emanates on the anode side. A hole transporting layer, a hole transporting and light emitting layer, a light emitting layer or the like is deposited adjacent to the anode.
However, problems arise if the anode is disposed in direct contact with an organic material layer such as a layer of hole transporting material such as triphenyldiamine (TPD), a light emitting layer of aluminum quinolinol complex (Alq3) and a hole injecting layer. The adhesion between the anode and the organic material layer and the efficiency of hole injection are exacerbated. Interfacial separation can occur to form non-light-emissive areas known as dark spots. The reduction of hole injection efficiency can deteriorate the performance of the organic EL device.